1. Field of the Invention
The present invention relates to an intermediate accessory, such as an intermediate lens, a bellows, and a rear converter, which is mounted or interposed between a camera body and an interchangeable lens. More particularly, the invention relates to such an accessory for use in a photographic camera system wherein various data that are inherent to the objective lens being used are transmitted from the objective lens to the camera body, the data are processed and the resultant data are used for automatic exposure control, automatic focusing, and various warnings and indications. The data may include the maximum and minimum F-numbers, the focal length and the shortest photographable distance of the lens, data indicative of the relationship between the direction of the rotation of a motor within a camera body for automatic focusing and the direction of the movement of the lens system, and data indicative of the relationship between the amount of rotation of the motor and the amount of the shifting of the image plane.
2. Description of the Prior Art
Generally, when an intermediate accessory, such as a rear converter, is mounted between an objective lens and a camera body, the minimum F-number and focal length of the entire optical system are determined by the optical parameters of the lens systems of the objective lens and the rear converter. Accordingly, those values of the F-number and focal length may be composite values depending on the configurations of both optical systems and are different from the values for the objective lens without intermediate accessory.
In view of this fact, U.S. Pat. Nos. 4,329,440 and 4,326,788 disclose camera systems wherein an objective lens is provided on its barrel with a signal member at a specific position in the circumferential direction thereof corresponding to the minimum F-number. The camera body is provided with a detection member for detecting the angular position of this signal member to enable transmission of the data of the minimum F-number value from the objective lens to the camera body, and a rear converter to be interposed therebetween is provided within its lens barrel, with a transmitting member which detects the position or location of the signal member of the objective lens, converts the position data to data corresponding to the minimum F-number as the composition of the F-number data of objective lens and rear converter lens system, and transmits the converted data to the detection member of the camera.
This construction enables transmission of correct information suitable for photographing, to the camera body, even when a rear converter is used. On the other hand, a device that makes use of the location of a physical member as described above for transmitting information, requires a large area for the transmission of a single data, resulting in a limitation of the number and kinds of transmissible data by way of the limited area around the mount plane. In addition, since operations or processing of data in the camera body is performed by an electrical circuit based on the data transmitted to the camera, means for converting this mechanically transmitted data into electrical signals is required so that mechanisms the camera mechanisms will be complicated in construction.
Accordingly, in a Japanese patent application which was filed by the assignee of the present application and laid-open with a laid-open No. 54-108628, a camera system is proposed wherein the barrel of an objective lens is provided with a ROM (Read only memory) which stores data inherent to the objective lens in the form of electrical signals and with a device for reading out the data, while the camera body is provided with a microcomputer which reads the data signals from the ROM and performs operations using the data signal.